Currently, optical fiber signal transmission is essential for configuration of a social infrastructure. For optical transmitters and receivers used in the optical fiber signal transmission, developments compliant with MSA (Multi-source Agreement) as a standard specification is centered for the purpose of stable supply of signals. Recently, developments based on a standard specification of SFP+ in MSA have been started in respective companies. In SFP+, although the speed of the main signal is as fast as 10 Gbps, no identifier for discrimination of data codes with respect to reception signals is contained within an optical module.
Accordingly, in SFP+, it is necessary to provide the above described identifier outside of the optical module, specifically on a unit as a connection destination of the optical module.
By the way, transmission characteristics such as dispersion characteristics and noise characteristics of an optical path connected to the optical module have an impact on the waveform of a reception signal input to the identifier. On the other hand, quality characteristics of the reception signal obtained as an identification result largely depend on the threshold setting of the identifier.
Japanese Laid-open Patent Publication No. 2004-15587 discloses a technology, in order to improve the quality characteristic of the reception signal, of calculating a threshold value from the output waveform of an amplifier of a receiver with a peak detector, a DC detector, and a bottom detector for optimization of the threshold value of an identifier.
However, the conventional technology does not consider optimization of the threshold value when an identifier is provided on a unit as a connection destination of the optical module.